Graphene, an allotrope of carbon forming a two-dimensional, atomic-scale, hexagonal lattice, has become useful for applications in flexible electronics due to its exceptional electrical, mechanical, and chemical properties. In order to realize practical applications of graphene, large-scale production methods such as chemical vapor deposition (CVD) on transition metal surfaces have been increasingly explored. In particular, copper has become a popular catalytic substrate due to its low carbon solubility at typical growth temperatures.
However, it has been observed that a strictly two-dimensional graphene system is often thermodynamically unstable, and frequently exists only through perturbations in a third direction. These fluctuations in the third direction generally result in a crumpled topography of the graphene sheet surface, such as “ripples” thereon. It is currently understood that graphene ripples may be associated with (a) the problem of thermodynamic stability of two-dimensional layers or membranes; (b) the thermal expansion coefficient difference between a metal substrate and graphene; and/or (c) the presence of grain boundaries on the metal substrate. As graphene surface topography has significant impact on its mechanical, electronic, magnetic, and chemical properties, understanding and controlling the formation of ripples is important for exploiting its excellent properties.
While continuous production methods for preparing a graphene sheet (such as roll-to-roll methods, where vapor containing carbon reacts on a horizontal substrate such as a copper foil) dramatically reduces production price, such methods often correspond with unwanted wrinkles or ripples on the grown graphene surface.
There is thus a need in the art for methods of manufacturing high quality and large surface area graphene, while reducing both production price and unwanted surface topography.